Homeostasis of the skin and its appendages relies on the continuous renewal of the epidermis and periodic renewal of the hair follicle epithelium throughout life from stem cells resident in these epithelia. While progress has been made in identifying these cells, the genetic mechanisms that regulate their specification as stem cells and the subsequent differentiation of their progeny to form the constituent cell types of the skin and its appendages in an orderly fashion remain poorly understood. This project examines the role of Helios, a member of the Ikaros gene family, in this process. The Ikaros family genes are critical to the development of hematopoietic stem cells and the subsequent progression of their progeny through the lineages that give rise to the lymphoid system. Our preliminary studies show that Helios is expressed in skin and interference with its function leads to profound defects in skin development and differentiation. It is our hypothesis that Helios activity is critical to the specification of stem cells in the skin and its appendages and to the orderly differentiation of their progeny. This project will test the role of Helios in development of the skin and its appendages. We will characterize the expression of Helios in more detail. A floxed allele of Helios will be employed in conjunction with ere recombinase lines to delete Helios function in different cell types in the epidermis and follicular epithelium of transgenic mice. This will allow us to identify critical time periods and cell types in which Helios acts and to assess the proximal effects of altering Helios function. Cells with altered Helios function will be partially purified by FACS from mice that express fluorescent proteins in different cell types in the skin and used to identify the genes whose expression changes in response to acute changes in Helios activity. A subset of these genes that represent direct targets of the regulatory activity of Helios will also be identified. These studies will impact our understanding of the normal and abnormal development of the skin and its appendages and the function of this gene family in the specification and function of stem cells of the integument.